Updated at 6:39 p.m. Eastern
Thick drifts of volcanic ash blanketed parts of rural Iceland on Friday as a vast, invisible plume of grit drifted over Europe, emptying the skies of planes and sending hundreds of thousands in search of hotel rooms, train tickets or rental cars.
The air traffic agency Eurocontrol said almost two-thirds of Europe's flights were canceled Friday, as air space remained largely closed in Britain and across large chunks of north and central Europe.
"The skies are totally empty over northern Europe," said Brian Flynn, deputy head of Eurocontrol, adding "there will be some significant disruption of European air traffic tomorrow."
Volcanic Eruption Grinds Modern World to a Halt
Volcano Ash Poses Threat to Global Business
Ash Disrupts U.S. Medevac Flights From War Zones
WHO: Falling Volcano Ash a Health Risk
Pain in the Ash: A Guide to Europe's Air Turmoil
The agency said at least 17,000 and as many as 18,000 of Europe's usual 28,000 daily flights were canceled Friday - twice as many as were canceled a day earlier.
About 280 flights between the U.S. and Europe were cancelled Friday, the International Air Transport Association said Friday evening. Usually 337 flights operate daily between the U.S. and Europe, according to the group. About 60 flights between Asia and Europe were cancelled.
CBS News Correspondent Richard Roth reports that, according to the Centre for Asia Pacific Aviation, more than 6 million passengers on Saturday could feel the ash cloud's disruption to global travel.
"The problem is that you're dealing with [thousands of] flights that were cancelled," CBS News Travel Editor Peter Greenberg told CBS Radio News from London. "You're now dealing with a multiple of that number that are out of sequence, meaning the planes and the crews aren't where they're supposed to be, so you're dealing with a 36 to 48 hour and perhaps even longer turnaround time to get crews to where the actual aircraft are to get them back in position."
The International Air Transport Association said the volcano was costing the industry .
Southern Iceland's Eyjafjallajokull glacier began erupting for the second time in a month on Wednesday, sending ash several miles into the air. Winds pushed the plume south and east across Britain, Ireland, Scandinavia and into the heart of Europe.
Gray ash settled in drifts near the glacier, swirling in the air and turning day into night. Authorities told people in the area with respiratory problems to stay indoors, and advised everyone to wear masks and protective goggles outside.
In major European cities, travel chaos reigned. Extra trains were put on in Amsterdam and lines to buy train tickets were so long that the rail company handed out free coffee.
Train operator Eurostar said it was carrying almost 50,000 passengers between London, Paris and Brussels. Thalys, a high-speed venture of the French, Belgian and German rail companies, was allowing passengers to buy tickets even if trains were fully booked.
Ferry operators in Britain received a flurry of bookings from people desperate to cross the English Channel to France, while London taxi company Addison Lee said it had received requests for journeys to cities as far away as Paris, Milan, Amsterdam and Zurich.
The disruptions hit tourists, business travelers and dignitaries alike.
Polish officials worried that the ash cloud could threaten the arrival of world leaders for Sunday's and his wife Maria in the southern city of Krakow.
So far, President Obama, Russian President Dmitry Medvedev and German Chancellor Angela Merkel are among those coming and no one has canceled. Kaczynski's family insisted Friday they wanted the funeral to go forward as planned but there was no denying the ash cloud was moving south and east.
Merkel had to go to Portugal rather than Berlin as she flew home from a U.S. visit. Norwegian Prime Minister Jens Stoltenberg managed to get a flight to Madrid from New York but was still not sure when or how he would get back home.
The military also had to adjust. Five German soldiers wounded in Afghanistan were diverted to Turkey instead of Germany, while U.S. medical evacuations for troops in Iraq and Afghanistan are being rather than to a care facility in Germany. The U.S. military has also stopped using temporarily closed air bases in the U.K. and Germany.
Aviation experts said it was among the worst disruptions Europe has ever seen.
"We don't have many volcanoes in Europe," said David Learmount of Flight International, an aviation publication. "The wind was blowing in the wrong direction."
In Iceland, torrents of water carried away chunks of ice the size of small houses on Thursday as hot gases melted the glacier over the volcano. Sections of the country's main ring road were wiped out by the flash floods.
More floods from melting waters are expected as long as the volcano keeps erupting - and in 1821, the same volcano managed to erupt for more than a year.
Small amounts of ash settled in northern Scotland and Norway, but officials said it posed little threat to health.
The ash cloud, drifting between 20,000 to 30,000 feet (6,000 to 9,000 meters) high and invisible from the ground, initially blocked the main air flight path between the U.S. east coast and Europe. On Friday, the cloud's trajectory was taking it over northern France and Austria and into eastern and central Russia at about 25 mph (40 kph).
Fearing that microscopic particles of highly abrasive ash could endanger passengers by , authorities shut down air space over Britain, Ireland, France, Denmark, Norway, Sweden, Finland and Belgium. That halted flights at Europe's two busiest airports - Heathrow in London and Charles de Gaulle airport in Paris - as well as dozens of other airports, 25 in France alone.
Air space restrictions were lifted, imposed or extended Friday as the cloud moved.
Flights were suspended at Frankfurt airport, Europe's third-busiest terminal, and at other German airports including Duesseldorf, Berlin, Hamburg, Munich and Cologne.
Irish aviation authorities reopened airports in Dublin and Cork and France allowed some planes to land in Paris. Sweden and Norway declared skies in the far north to be safe but kept a lockdown on flights to both capitals - Stockholm and Oslo.
Aviation officials said the air over England would remain closed to flights until at least 8 a.m. EDT Saturday, and British Airways announced it was canceling all of its flights to and from London airports late Friday and on Saturday.
In France, airports in Paris and about 20 other locations in northern France will remain closed until at least midday Saturday.
Belgium extended its flight restrictions until late Saturday morning.
Switzerland, Slovakia, Croatia and Hungary closed their airspace, and Poland expanded its no-fly zone to most of the country, excluding Krakow. Belgium extended its flight restrictions until late Saturday morning.
Iceland, a nation of 320,000 people, sits on a large volcanic hot spot in the Atlantic's mid-oceanic ridge and has a history of devastating eruptions. One of the worst was the 1783 eruption of the Laki volcano, which spewed a toxic cloud over Europe, killing tens of thousands.
© 2010 CBS Interactive Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.